A serine/threonine phosphatase 1 of Streptococcus suis type 2 is an important virulence factor

Streptococcus suis is regarded as one of the major pathogens of pigs, and Streptococcus suis type 2 (SS2) is considered a zoonotic bacterium based on its ability to cause meningitis and streptococcal toxic shock-like syndrome in humans. Many bacterial species contain genes encoding serine/threonine protein phosphatases (STPs) responsible for dephosphorylation of their substrates in a single reaction step. This study investigated the role of stp1 in the pathogenesis of SS2. An isogenic stp1 mutant (Δstp1) was constructed from SS2 strain ZJ081101. The Δstp1 mutant exhibited a significant increase in adhesion to HEp-2 and bEnd.3 cells as well as increased survival in RAW264.7 cells, as compared to the parent strain. Increased survival in macrophage cells might be related to resistance to reactive oxygen species since the Δstp1 mutant was more resistant than its parent strain to paraquat-induced oxidative stress. However, compared to parent strain virulence, deletion of stp1 significantly attenuated virulence of SS2 in mice, as shown by the nearly double lethal dose 50 value and the lower bacterial load in organs and blood in the murine model. We conclude that Stp1 has an essential role in SS2 virulence.